Referring to FIG. 2, an easy open end (also called an easy open cap) includes a body hook 6, a chuck wall 7, a panel 8, a score 11, a rivet 10, and a tab 9. The material of the easy open end may be an aluminum sheet or a steel sheet on which coating is applied or an organic resin film is laminated. Aluminum is frequently used as the material. The coated or laminated steel sheet is inexpensive as the material. However, after the end is processed, repair coating is necessary. Thus, the steel sheet is not economically advantageous. For these reasons, the steel sheet is not frequently used.
Under such circumstances, various trials to omit the repair coating of the steel-sheet easy open end have been made, by improving the processing method of the end and by using a laminated steel sheet suitable for the processing method.
FIG. 7 is a cross-sectional view showing a die for forming a score (cut groove) of an easy open end according to related art. Referring to FIG. 7, a V-shaped score die is used in the related art. Hence, the score (cut groove) for opening an end has a V-shaped cross section. When the material is the laminated steel sheet, the V-shaped score die breaks the laminated film and an iron portion is exposed. To secure corrosion resistance of the exposed portion, the repair coating has been necessary after scoring.
Patent document 1 tries to omit the necessity of the repair by using polyester resin and forming a score by two-step press (compound press) without using the conventional V-shaped score die.
Patent document 2 tries to omit the repair by using a curved-surface die for scoring to prevent the film from being broken.
Patent document 3 tries to improve openability and to omit the repair by specifying the cross-sectional shape of a curved-surface die used for scoring.